Printed circuit boards (PCBs) usually include solder mask coatings applied to the copper traces for protection against oxidation, and to prevent solder bridges being generated between adjacent solder pads. The solder mask coating is formed by a solder mask ink. Organic solvents, such as propylene glycol methyl ether acetate (PGMEA), methy ethyl ketone (MEK), ethylene glycol monobutyl ether (BCS), or toluene, are generally used in process of making the solder mask ink. The organic solvent is harmful to the environment. When using the solder mask ink to make PCB, an alkaline aqueous solution or an organic developer is used in developing process, which is also harmful to the environment.